The authors have recently defined the clinopathological entity of a mucin-producing bile duct tumor (MPBT), and divided MPBT into two distinct subtypes: ‘columnar-type’ and ‘cuboidal-type’ MPBT. Mucin core protein 6 (MUC6), which is present in normal pyloric glands, had higher expression levels in cuboidal-type tumors than in columnar-type tumors. In the pyloric glands, a carbohydrate antigen detected by monoclonal antibody HIK1083 (CA/HIK1083) is also expressed. In order to evaluate the coexpression pattern of MUC6 and CA/HIK1083 in MPBT, expression profiles were evaluated in 38 surgically excised mucin-producing bile duct carcinomas (MPBC; cuboidal-type, n = 15; columnar-type, n = 23), using immunohistochemistry. The staining rate was graded as follows: –, <5% of neoplastic cells stained; +, 5% to <20%; + +, 20% to <50%; + + +, ≥50%. In cuboidal-type MPBC, MUC6 was positive in all cases (+ + +, 13/15; + +, 1/15; +, 1/15), whereas CA/HIK1083 was negative in all cases (–, 15/15; P < 0.0001). In columnar-type MPBC, MUC6 was positive in 65% of cases (+ + +, 6/23; + +, 8/23; +, 1/23; –, 8/23), and CA/HIK1083 was positive in 52% (+ +, 3/23; +, 9/23; –, 11/23; not significant). Our results clearly demonstrate that cuboidal-type MPBC have an aberrant pyloric glandular phenotype, that is, MUC6+/CA/HIK1083–. This unique profile may be related to different outcomes of patients with MPBC.